Screening visitors after rather than before they board boats to the Statue of Liberty and Ellis Island is nuts. But what do you expect when you disregard Ray Kelly’s advice on security issues?

On Monday, the city’s police commissioner and the state’s senior senator, Chuck Schumer (D), blasted a National Park Service plan to scrap the Battery Park screening site and allow visitors aboard boats to Liberty and Ellis Islands unchecked. Only after they land at Ellis would they be screened. Which might be too late.

“It’s like screening people after they get off airplanes,” Schumer rightly says. But the Park Service is ignoring these warnings from him and Kelly.

This isn’t the first time officials have bypassed Kelly on security. After 9/11, the Pataki folks drew up a blueprint for rebuilding the World Trade Center without consulting the police. Big mistake: After Kelly cited its key security flaws, the plan had to be re-done, which set it back more than a year.

Today there’s a long line of would-be police commissioners hoping to override Kelly — starting with federal Judge Shira Scheindlin, who’s about to rule in the just-concluded stop-and-frisk case. Plaintiffs want her to appoint a monitor to oversee the NYPD, and she’s already shown notable bias in their favor. Another mistake.

Then there’s the City Council. It’s got not one but two bills to steal control of the police. The first would set up an inspector general for the cops whose recommendations would have huge sway no matter what Kelly thought. Really serious mistake.

The second bill would target supposed racial profiling by police — to the point, Mayor Bloomberg says, where any male, youth or minority member they stop could sue, citing police activity that has a “disparate impact” on that person’s “group.” Cops would have to refrain from making vital stops (and maybe arrests) or face a judge’s censure, including the prospect of a monitor. Potentially catastrophic mistake.

The Democratic mayoral wannabes are all second-guessing the commish, too. Meanwhile, Kelly’s keeping crime low and the city safe from terror. Are these pols really willing to set a different course — and take the blame for any resulting tragedies?